ANCHORAGE, Alaska — The FBI confirms the powdery substance sent to members of Alaska’s congressional delegation was a mixture of concrete.

The envelopes were opened Monday at the offices of Sens. Mark Begich and Lisa Murkowski in Fairbanks and Rep. Don Young in Anchorage.

Eric Gonzalez, an FBI spokesman in Anchorage, said agents contacted the sender of the letters in Arizona and discovered there was no malicious intent. The person sent samples of a concrete mixture, something the person said would work well in a cold environment.

Testing confirmed there were no hazardous materials. The FBI is not releasing the sender’s identity because there was no criminal malice.

The Fairbanks federal building was evacuated and the floor holding Young’s Anchorage office was closed after the substance was found.